Richard Beigel John Gill Ulrich Hertrampf Counting Classes: Thresholds, Parity, Mods, and Fewness. 49-57 1990 conf/stacs/1990 STACS db/conf/stacs/stacs90.html#BeigelGH90 http://dx.doi.org/10.1007/3-540-52282-4_31